Netpbm is a toolkit for conversion of images between a variety of
different formats, as well as to allow a few basic image operations.
Netpbm is based on the widely spread Pbmplus package (release: 10 Dec
91). On top of that, a lot of improvements and additions have been
made. After the latest release of Pbmplus, a lot of additional filters
have been circulating on the net. The aim of Netpbm was, to collect
these and to turn them into a package. This work has been performed by
a group of programmers all over the world.

Log message:
*: Move SUBST_STAGE from post-patch to pre-configure
Performing substitutions during post-patch breaks tools such as mkpatches,
making it very difficult to regenerate correct patches after making changes,
and often leading to substituted string replacements being committed.

Log message:
graphics/*: remove redundant :Q modifiers
pkgsrc doesn't support PREFIX with spaces or other special characters.
Therefore it is not necessary to add the :Q modifier to this variable
and several others.